cryptography

cryptography

Computers Any of various mathematical techniques for encrypting and decrypting data in order to keep it private when transmitted or stored electronically.

The process or skill of communicating in or deciphering secret writings or ciphers.

Secret writing.

Related Forms:

cryp′to·graph′ic

adjective

cryp′to·graph′i·cal·ly

adverb

cryptography

Noun

(usually uncountable, plural cryptographies)

The discipline concerned with communicationsecurity (eg, confidentiality of messages, integrity of messages, sender authentication, non-repudiation of messages, and many other related issues), regardless of the used medium such as pencil and paper or computers.

In many languages, though less so in English, cognates to "cryptology" are also used with the meaning given above, and even preferred.

Related to cryptography but distinct, steganography is the art and science of writing hidden messages in such a way that no-one apart from the sender and intended recipient even realizes there is a hidden message.

Origin

crypto- +‎ -graphy

cryptography - Computer Definition

From the Greek kryptos, meaning hidden, and graphos, meaning written.The art or science, or system, of writing messages in code, or cipher, to disguise, and thereby secure, the content. When encrypted, a plain text message can be revealed only through the use of the key to the code. Cryptography does not mask the existence of the message, but does disguise its content. See also steganography.

The conversion of data into a secret code for transmission over a public network. Today, most cryptography is digital, and the original text ("plaintext") is turned into a coded equivalent called "ciphertext" via an encryption algorithm. The ciphertext is decrypted at the receiving end and turned back into plaintext.
Keys Are the Key
The encryption algorithm uses a "key," which is a binary number that is typically from 40 to 256 bits in length. The greater the number of bits in the key (cipher strength), the more possible key combinations and the longer it would take to break the code. The data are encrypted, or "locked," by combining the bits in the key mathematically with the data bits. At the receiving end, the key is used to "unlock" the code and restore the original data.

Secret Vs. Public Key

Secret key cryptography and public key cryptography are the two major cryptographic architectures.
Secret Keys - Symmetric System
The first method uses a secret key, such as the DES and AES algorithms. Both sender and receiver use the same key to encrypt and decrypt. This is the fastest computation method, but getting the secret key to the recipient in the first place is a problem that is often handled by the second method.
Public Keys - Asymmetric System
The second method uses a two-part key, such as RSA and El Gamal. Each recipient has a private key that is kept secret and a public key that is published for everyone. The sender looks up or is sent the recipient's public key and uses it to encrypt the message. The recipient uses the private key to decrypt the message and never publishes or transmits the private key to anyone. Thus, the private key is never in transit and remains invulnerable.
Both Are Used Together
Secret key and public key systems are often used together, such as the AES secret key and the RSA public key. The secret key method provides the fastest decryption, and the public key method provides a convenient way to transmit the secret key. This is called a "digital envelope." For example, the PGP e-mail encryption program uses one of several public key methods to send the secret key along with the message that has been encrypted with that secret key (see PGP).
Get Faster - Get Stronger
It has been said that any encryption code can be broken given enough time to compute all permutations. However, if it takes months to break a code, the war could already be lost, or the thief could have long absconded with the money from the forged financial transaction. As computers get faster, to stay ahead of the game, encryption algorithms have to become stronger by using longer keys and more clever techniques. See XOR, AES, DES, RSA, plaintext, digital signature, digital certificate, quantum cryptography, steganography and chaff and winnow.

Secret Key Vs. Public Key

The secret method uses the same key to encrypt and decrypt. The problem is transmitting the key to the recipient in order to use it. The public key method uses two keys: one kept private and never transmitted, while the other is made public. Very often, the public key method is used to safely send the secret key to the recipient so that the message can be encrypted using the faster secret key algorithm.

Some Public History About Secret Methods

The following is reprinted with permission from RSA Security, Inc.
In 1518, a Benedictine monk named Johannes Trithemius wrote "Polygraphiae," the first published treatise on cryptography. Later, his text "Steganographia" described a cipher in which each letter is represented by words in successive columns of text, designed to hide inconspicuously inside a seemingly pious book of prayer.
Polygraphiae and Steganographia attracted a considerable amount of attention not only for their meticulous analysis of ciphers but more notable for the unexpected thesis of Steganographia's third and final section, which claimed that messages communicated secretly were aided in their transmission by a host of summoned spirits.
As might be expected, Trithemius' works were widely renounced as having magical content - by no means an unfamiliar theme in cryptographic history - and a century later fell victim to the zealous flames of the Inquisition during which they were banned as heretical sorcery.

Sentence Examples

Cryptography had a great fascination for Wheatstone; he studied it deeply at one time, and deciphered many of the MSS.

This non-Semitic system, which is found, in many instances, on alternate lines with a regular Semitic translation, in other cases in opposite columns to a Semitic rendering, and again without any Semitic equivalent at all, has been held by one school, founded and still vigorously defended by the distinguished French Assyriologist, Joseph Halevy, to be nothing more than a priestly system of cryptography based, of course, on the then current Semitic speech.

This cryptography, according to some of the Halevyans, was read aloud in Semitic, but, according to other expositors, the system was read as an " ideophonic," secret, and purely artificial language.

Facts of this character taken by themselves would perhaps be sufficient to convince most philologists that in Sumerian we have an arbitrarily compounded cryptography just as Halevy believes, but these facts cannot be taken by themselves, as the evidences of the purely linguistic basis of Sumerian are stronger than these apparent proofs of its artificial character.

Certainly no cryptography based exclusively on Semitic could exhibit this sort of interchange.